Atrial fibrillation is one of the most common cardiac arrhythmia. Health consequences associated with atrial fibrillation include decreased cardiac output, less regular ventricular rhythm, the formation of blood clots in the atrial appendages, and an increased incidence of stroke. While some drugs are available for the treatment of atrial fibrillation, they have a number of side effects which reduce their therapeutic utility.
Unlike patients afflicted with ventricular fibrillation, patients afflicted with atrial fibrillation are conscious. The pain associated with the administration of the defibrillation shock can be severe, and there is a need for means of carrying out atrial defibrillation in a manner that is less painful to the patient being treated. One means for reducing the pain associated with atrial defibrillation is to administer multiple shocks, but the administration of multiple shocks typically requires the implantation of additional electrodes.
For ventricular fibrillation, the patient is generally unconscious, the condition is life threatening, and the pain associated with shock is not an issue. It is, however, desirable to reduce the shock strength administered so that the size of the implantable device can be reduced, or to administer shocks in a manner that will decrease the likelihood of recurrence of fibrillation. To meet these objects, it is desirable to administer multiple shocks. Again, the administration of multiple shocks requires the implantation of additional electrodes.
Numerous patients are afflicted with both ventricular and atrial arrhythmias. For such patients, it would be exceedingly desirable to provide a single device that can carry out both atrial and ventricular defibrillation with minimum shock strength, and with minimal surgical intervention.
In view of the foregoing, a first object of the invention is to provide an implantable system for treating cardiac arrhythmia that does not require invasion of the chest cavity for the placement of epicardial electrodes.
A second object of the invention is to provide an implantable cardioversion system wherein the probability of successful cardioversion on administration of the first cardioversion pulse is enhanced, particularly in the case of ventricular fibrillation.
A third object of the invention is to provide an implantable system for treating cardiac arrhythmia that enables reduction of cardioversion, and particularly defibrillation, shock strength.
A fourth object of the present invention is to provide methods and apparatus for carrying out atrial defibrillation that will reduce the pain associated therewith.
A fifth object of the present invention is to provide methods and apparatus for carrying out atrial defibrillation that will reliably treat atrial fibrillation.
A sixth object of the present invention is to provide methods and apparatus for treating atrial fibrillation that minimizes the extent of the surgical intervention involved in implanting the necessary defibrillation electrodes, and minimizes the complexity involved in implanting the necessary defibrillation electrodes.